Operating instructions

3 Functions Issue 10/06

MICROMASTER 420 Operating Instructions

118 6SE6400-5AA00-0BP0

3.7.1.3 USS bus configuration via COM link (RS485)

In order to ensure disturbance-free USS operation, the bus cable must be

terminated at both ends using bus terminating resistors. In this case, the bus cable

from the first node up to the last node should be considered as

one bus cable – so

that the USS bus should be terminated twice. For the

first bus node [device] (e.g.

master) and

last bus node [device] (e.g. drive converter), th bus terminating

resistor must be switched-in.

NOTE

♦ When supplied, the bus terminating resistors are not switched-in!

♦ Please note that you only switch-in the bus terminating at the first bus node

[device] and last bus note! The

bus terminating resistors should be always set

when the system is powered-down!

♦ Data transfer errors on the bus are possible!

In active bus operation, nodes where the terminating

resistor is switched-in,

must always be powered-up. The terminating resistor draws the voltage from

the connected device. This is the reason that the terminating resistor is no

longer effective when the node is powered down .

The following diagram shows the structure of a bus connection through terminals

14, 15:

Screening

Screening Screening

Potential equilization cable

RS485 terminator

Master

0 V

(M)

• a terminating resistor must be connected at the first and last node on the bus cable

• no bus termination for other nodes

Fig. 3-40 Connecting the USS bus cable